Field of Invention
The present invention relates to a navigation server with a function of communicating with a plurality of navigation clients serving as a mobile station and a system composed of the navigation server and the plurality of navigation clients.
Description of the Related Art
There has been proposed a technique for detecting a level of traffic jam depending on vehicle speeds from a vehicle speed, a prescribed speed, a movement history (set according to a level of traffic jam), a prescribed distance, and a combined determination distance (refer to Patent Literature 1: International Publication No. WO 2008/007663). Furthermore, there has been proposed a technique for determining a level of traffic jam by allocating traffic jam level information according to the maximum vehicle speed to a link in a starting-end reference-point distance predetermined from the starting point of the link, if a link length is within a predetermined range (refer to Patent Literature 2: International Publication No. WO 2009/025359). Still furthermore, there has been proposed a technique in which past and present traffic jam information at a prescribed place is obtained to grasp increase/decrease tendency of the traffic jam and notification is performed (refer to Patent Literature 3: International Publication No. WO 2008/010408). Still yet furthermore, there has been proposed a technique for displaying traffic jam information on a map of a display unit in a superimposed manner to grasp the spread of the whole traffic jam range (refer to Patent Literature 4: International Publication No. WO 2014/103079). Still yet furthermore, there has been proposed a technique in which a vehicle detector calculates traffic amount based on the number of vehicles in the upstream and downstream intervals to presume the number of vehicles in an interval (refer to Patent Literature 5: Japanese Patent Laid-Open No. 2014-137696)
In a mobile station, since traffic state is displayed or used as a unit of links, the traffic state displayed in the mobile station may deviate from an actual traffic state in such a case where, for example, traffic jam occurs in a part of the link but traffic is smooth in another part. Thus, as the link becomes longer, the tendency of the traffic state in a part of the link differing from another part may be stronger. As a result, reliability of the traffic state displayed in the mobile station may be compromised.
The problem to be solved by the present invention is to provide a navigation server capable of improving reliability or estimation accuracy of information about traffic state provided for a user in view of the present traffic state.